We present here a wide review of the existing models accounting for surface potential decay, developed in various areas of electrostatics. Several polarization or transport processes may be involved. Though most of the models initially stemmed from electrostatics and semiconductor physics, around the notion of mobility, experiments on polymers often require "thermodynamic" models, describing progressive charge detrapping. Different physical processes likely to be involved in the potential decay (dipolar relaxation, induced conductivity, dispersive transport, slow detrapping) can lead in disordered materials to the same time response, the challenge being to design inventive procedures to distinguish them. A particular attention will be given to the application of these models to polyimide and fluorinated ethylene propylene. The specific case of radiation-induced conductivity in these materials will also be examined in detail.